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The effect of structure on the sorption kinetics of water and of various organic solutes into polyimide (PMDA‐ODA) thin films was studied. The major techniques employed include measurements of sorption kinetics, density, and dielectric relaxation. More solute uptake, lower densities and higher diffusivities were observed for films cured at lower temperatures. By measuring both changes of mass and of density, the volume expansion of the polymer due to each solute was obtained; this was found to be proportional to the molar volume of the solute. The two dielectric relaxation peaks (denoted by γ1 and γ2) due to water (and other solutes) were studied in detail to obtain the relevant activation energies and the separate dipole moments. While water and methylene chloride appear in both γ1 and γ2 configurations, methyl and ethyl alcohol appear mainly as γ2, while acetic acid is primarily γ1. It was concluded that the γ1 configurations are relatively homogeneously distributed throughout the polymer, involving loose bonding to the polymer structure, while the γ2 configurations involve small clusters, probably chains of molecules. © 1993 John Wiley & Sons, Inc.

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Complex materials are known to show two regions of ac electrical behavior. In the high-temperature/lowfrequency domain, they show power-law frequency dependence of the conductivity known as ''universal dielectric response,'' or UDR, while at low temperatures/high frequencies they show ''nearly constant loss,'' or NCL behavior, which persists down to cryogenic temperatures. The present paper seeks to examine the corresponding behaviors of ''simple'' systems, i.e., dilute systems of the classical type in which a relatively small number of defects are involved. Three systems studied here are oxygen-ion conductors: CeO 2 doped with Gd 3ϩ and with Y 3ϩ , as well as CaTiO 3 doped with Al 3ϩ . In each case, we proceed from dilute to concentrated doping levels. Also studied in very dilute concentrations are NaCl:Sm 3ϩ ͑a Na ϩ conductor͒ and KTaO 3 :Cu 2ϩ ,H ϩ ͑a protonic conductor͒. It is found that in the UDR regime, the simple materials show very much the same behavior as the complex, suggesting that UDR relaxation is intrinsic to the hopping process. A striking result is that the onset frequency of dispersive conductivity corresponds to the mean jump frequency of all carriers, both bound and free. In contrast to the UDR regime, NCL behavior is only shown by complex materials; simple materials show discrete ͑Debye-type͒ relaxations that are due to off-center configurations that relax by small rocking-type motions. As the concentrations increase, these relaxations smear out into a broad distribution that gives rise to NCL behavior.

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